The Lowdown on Fasting: Is the Ultimate Diet Good or Bad for You?

Dieting has been a "thing" for as long as humans have been eating, it would seem. And certainly since they’ve been overeating. High carb, low carb, Paleo, Atkins, Scarsdale—so many diets, so little willpower. The most extreme diet of all, fasting in order to lose weight and get healthy, has been popular off and on for years. For good reason too. It makes sense. You can’t get much lower calorie than no calorie. In truth, fasting for short periods of time can be a very effective way to lose weight and even gain other additional benefits. The danger is in going too far.


What happens when you fast? During the six-hour period after you stop eating, your body breaks down your last meal into glycogen for storing, and glucose for energy, with about 25% of it going to your brain. After six hours and up to 72 hours (three days), the glycogen from your meal has been used up and your body starts converting fat into energy. Big problem, though—this fat energy source is not available to the brain, so it needs to get by on whatever is left of your last meal. After 72 hours, the body realizes it needs to get some energy to the brain, and begins breaking down muscle tissue into glucose. And without nutrition coming in in the form of vitamins, minerals and other food-based needs, other bodily systems start tripping up. The immune system first, overall energy, etc. Starved for glucose, the brain grows foggy. Finally, after as long as 70 days, death comes knocking.

Of course, nobody is suggesting fasting to this extreme, but it is important to realize that fasting can lead a minority of people into the spiral of anorexia, leading to just that extreme.

The most popular fasting diet today is known as intermittent fasting, and followed carefully, it does have its positive outcomes. On an intermittent fast, you may cap your caloric intake over the week, or may eat one day and fast the next. Here are some of the healthful benefits you may experience.

1. Changes body function.

During an intermittent fast, your body chemistry can be altered. Your insulin level will drop, which will trigger fat-burning. Levels of human growth hormonwill increase as much as five times, which can burn fat and increase muscle mass. Cells will work to remove waste products. Even down to the molecular level, your body changes in ways that can actually protect you from disease.

2. Increases metabolism.

Intermittent fasting, due to the bodily changes above, actually increases the metabolic rate in your body, and your metabolism will burn fat faster, by up to 14%. With the decreased calorie intake from fasting plus the increased metabolism, you can lose up to 8% of your weight over 24 weeks. Moreover, a significant chunk of that weight loss is in the belly, the area of the body where studies have shown it is most harmful to be overweight (anything over 40 inches in men and 35 inches in women is considered abdominal obesity).

3. Lowers risk of Type 2 diabetes.

As noted above, intermittent fasting reduces insulin level in the blood. Studies have shown a reduction of up to 6% in blood sugar while fasting, with insulin level reduced by up to 31%. Studies in rats have shown intermittent fasting protects against kidney damage, a common problem in diabetics. These studies have been more conclusive in men than women, however.

4. Offers protection from free radicals and inflammation.

Volatile molecules called free radicals are prime suspects in the aging and chronic disease processes. Fasting has been shown to help the body fight off free radicals, and additionally, resist inflammation, another strong suspect in the progression of chronic diseases.

5. Offers protection from heart disease.

Although mostly done on animals, not humans, studies have indicated a positive effect of intermittent fasting on the health of the heart. Risk factors such as LDL cholesterol, blood sugars, inflammation, blood pressure, and triglycerides have all been improved during a fast.

6. Offers protection from cancer.

Animal studies have shown that intermittent fasting may be a protection against cancer. Fasting may also reduce some of the side effects of chemotherapy. (A very big caveat: weight loss in cancer patients is a huge problem that often contributes to health decline. Adequate nutrition is paramount in people who are fighting cancer.)

7. Good for the brain.

In addition to the positive effects intermittent fasting has on brain health due to insulin level reductions, free radical protection, and blood sugar reductions, animal studies have also shown an increase in the growth of new nerve cells, protection against stroke brain damage, and an increase in BDNF, a brain hormone that, when deficient, has been associated with depression, among other things. Intermittent fasting has also shown hopeful signs in animal studies of delaying the onset of Alzheimer’s disease.

8. Lengthens lifespan.

Just as caloric restriction has been shown to increase the lifespan of lab animals, intermittent fasting has yielded similar results. In one study, a mouse on a day-on, day-off fast lived 83% longer than the control mice.

It’s important to note that many of the positive effects of intermittent fasting have been shown on animals, not humans, so further studies would need to bear out the results on actual people. There are also negative effects to consider. Here are some of them:

  • Less nutrition: The less you eat, the fewer nutrients your body has to maintain optimum health.
  • Muscle loss: As noted above, fasting starts burning fat but moves on to muscles after a period of time.
  • Poor sleep: Hungry people often sleep poorly, and poor sleep has been associated with a myriad of physical and mental health problems.
  • Rebound overeating: Rebounds are only good in basketball. Many intermittent fasters daydream about food during their day off and compensate by overeating on their day on.

As always, it is a good idea to consult your doctor before trying anything as drastic as a fast, even a short one.

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